Peter Espada, the Republican-backed candidate on the Arlington County Board, said last night the board's agreement to float revenue bonds to finance the construction of a $30 million garage could place the county "in the soup" financially.

Espada, who is running as an independent, said in a debate with his Democratic rival, incumbent John G. Milliken, that county officials were "too optimistic" in projections for the number of motorists who would park at the 4,100-space structure at the planned Pentagon City Mall. Espada said the projections included patrons of a mall arts center that he thinks will not be well attended.

Milliken said in the debate before the Old Dominion Civic Association that Espada was wrong in suggesting the board had already approved a cultural center for the mall. The board has appointed a consultant and citizens committee to study whether to build a cultural center and stage there.

Espada, who is an economist with the General Accounting Office, said he thinks the garage project is "going to be endangered," and added that if the garage went bankrupt, the county would be obligated to rescue it. "I'm afraid we've placed our bond rating at risk."

Milliken, who is chairman of the Metro board, defended the board's decision, made in August, to float tax-exempt, low-interest bonds for the six-story parking project, to be operated by the county. He said the garage is "a good joint project" with the mall's developers, Rose Associates and Melvin Simon Associates.